Abstract
We monitored the radioligand-binding characteristics of thyrotropin-releasing hormone (TRH) receptors, functional activity of Gq/11α proteins, and functional status of the whole signaling cascade in HEK293 expressing high levels of TRH receptors and G11α. Our analyses indicated that disruption of plasma membrane microdomains by cholesterol depletion did not markedly influence the binding parameters of TRH receptors, but it altered efficacy of signal transduction. The functional coupling between TRH receptor and Gq/11α was assessed by agonist-stimulated [35S]GTPγS binding, and results of these measurements pointed out to significantly lower potency of TRH to mediate G protein activation in the plasma membrane fraction isolated from cholesterol-depleted cells; there was a shift in sensitivity by one order of magnitude to the higher concentrations. A markedly lower sensitivity to stimulation with TRH was also observed in our experiments dealing with determination of hormone-induced Ca2+ response. These data suggest that the intact structure of plasma membranes is an important optimum signal transduction initiated by TRH receptors and mediated by Gq/11α proteins.
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